Field-sensitive rheological fluids are compositions that generally include dielectric and/or magnetic particles suspended in a base fluid, and that show a change in viscosity when in the presence of an electric or magnetic field, respectively. Such field-sensitive rheological fluids are referred to in the art as “smart” fluids. In such fluids these particles are polarized in the presence of the applied field. The particles interact by aligning and orienting to form chain-like and/or lattice-like structures within the base fluid, aligned to the field. In turn, the aligned particles cause an increase in the effective viscosity of the bulk fluid. Removal of the field causes the particles to de-orient and to adopt an amorphous configuration, and hence, viscosity in turn decreases.
Typically, such field-sensitive rheological fluids include electrorheological fluids of polarizable materials with a low conductivity and a high dielectric constant, such as low molecular weight phenolic/phenolate oligomers, salts of (meth)acrylate oligomers and polymers, and other such materials, or magnetorheological fluids of ferromagnetic particles suspended in a base fluid such as a silicone or mineral oil. However, there remains a need for field-sensitive rheological fluids with improved properties such as a greater range of effective viscosity for a given electrical field strength and loading of the polarizable or ferromagnetic materials, and a faster response time as well as high temperature performance.